1. Field Of The Invention
This invention relates to an exercise device for exercising all of the major muscles comprising the upper and lower abdomen, without putting undue stress on the lumbar and cervical spinal discs and the muscles comprising the lower back and hip flexors.
It is well-known in the fitness industry that exercises which can optimally strengthen and tone the principal muscles in the abdominal region preferably are specific to particular muscles and/or to portions of those muscles.
The principal abdominal muscles include the rectus abdominus, obliquus internus abdominis and obliquus externus abdominis, which are more fully described as follows:
1. The rectus abdominus muscles are a pair of long flat muscles, one on either side of the navel, which extend along the whole length of the front of the abdomen from the lower rib cage to the front of the iliac and pubic bones of the pelvis. The rectus abdominus muscles are interconnected by the linea alba, a band of fibrous connective tissue.
2. The obliquus externus abdominis muscles (external obliques) are broad, thin, flat muscles situated on the lateral and anterior parts of the abdomen and attached by fibrous connective tissue to the abdominus rectus. They extend from the medial margins of the lower rib cage and are directed outwardly toward the rim of the iliac bone of the pelvis.
3. The obliquus internus abdominis muscles (internal obliques) are thinner and smaller than the obliquus externus muscles. The internal obliques lie beneath and transversely to the external obliques. The internal obliques extend from the lateral margins of the lower rib cage and are directed inwardly toward the rim of the pelvic iliac bone. The internal obliques are also attached to the abdominus rectus muscles by fibrous connective tissue.
The upper portion of the rectus abdominus can be effectively exercised by performing repetitions of "sit-ups" using the "crunch" technique. In this context, "crunch" refers to the motion in which the trunk of the human body is raised from a supine position, i.e.,, flexed, in a curling motion, while the spine is flexed so that the anterior portion of the spine is concave while the posterior portion of the spine is convex, and with the legs remaining straight or bent. The lumbar spine movements are predicated predominately by the orientation of the facet joints. The facet joints are true diarthrodial joints complete with synovium and joint capsules. In the lower lumbar spine the facet orientation is predominately in the sagital plane and less and less sagitally oriented toward the coronal plane angulation of the thoracic spine facets toward the upper lumbar spine.
The primary movement in the lumbar spine is therefore flexion and extension with rotation limited when the facets are engaged. As the front flexes forward, the facets are disengaged in the mid-range of flexion thereby permitting slight vertebral rotation. As the trunk flexes past the mid-range of trunk flexion, the facet joints are once again engaged thereby restricting the extent of vertebral rotation. As described in H. F. Farfan, Mechanical Disorders of the Lower Back, Lea & Febizer (1973), at pages 31-32 and 43-44, the facet joints of the lumbar spine have a vertical orientation, and the joint surfaces face each other and are almost parallel, but with a slight inclination to the anterior-posterior (A-P) plane. In successively lower lumbar levels, the facets assume an increasing reorientation so that joint surfaces of superior facets at the lumbosacral level face upwards, inwards and backwards. The orientation of the facets may be described as increasing inclinations, with descent down the spine of the facet joint, to two planes at right angles to each other. Because the surfaces of the joints have compound curvatures and it is therefore very difficult to assign an angle or plane of orientation for a given joint. Moreover, there is considerable variation in orientation from individual to individual. When the intervertebral joints are subjected to the stress of weight-bearing or of motion, small movements of the joints, known as " strain deflections" result. The point about which a given joint moves is the center of rotation. However, because this point may change with the movement, the point is referred to as "the instantaneous center of rotation." As emphasized in Farfan, it is "generally conceded that it is virtually impossible to have a pure movement in any of the three principal planes. The orientation of the facet surfaces generally does not coincide with the plane of the motion and therefore modifies the motion of the intervertebral joint. This is more certainly true of rotation than it is for flexion or extension. In an individual with symmetrical vertebrae, movements in the A-P plane may be free of either lateral bend or rotation. However, rotation is not possible without some degree of flexion and lateral bend." Thus, with reference to Farfan, it may be seen that the "crunch" motion, even in an individual with a symmetric spine, defines a complex curve or arc for a given joint as the spine is rotated through its entire range of motion. The profile of the spine itself, as it is rotated through the entire range of motion, also defines a family of complex curves. At any single instant, the locus of points on each joint of the spine will define a complex curve which, at each point, is orthogonal to the complex curve defined by the joint itself as it rotates.
The lower portion of the rectus abdominus can be effectively exercised by performing repetitions of the "knee-up" exercise in which the knees are lifted in an arcing motion toward the chest wall. "Knee-up" exercise refers to that motion of rotation of the legs, with the knees facing up and bent, and while the person is lying on the ground or floor.
The external obliques and internal obliques are best exercised by performing repetitions of a twisting, or rotary, crunch motion. Such a motion occurs during a sit-up exercise with the torso alternately twisted to the right and left, thereby pulling into action, respectively, the right obliquus externus and left obliquus internus, and the left obliquus externus and right obliquus internus.
As conventionally performed, these exercises are not without hazard and inconvenience. For example, performing sit-ups while keeping the legs straight risks injury and pain due to undue stress on the lower back regions. There is also danger of straining the hip flexor muscles, difficulty of controlling or adjusting muscular resistance, and, in some circumstances, discomfort and inconvenience associated with lying on the floor. Performing knee-ups in the conventional fashion also risks injury to the lower back and hips. Unless the knees are kept bent, the back is always curved and the abdominal muscles are tensed, thereby increasing the stress to the lower spine. This is the purpose for adopting a knees-bent posture in the conventional crunch technique for doing sit-ups. Furthermore, extreme twisting of the torso while performing rotary sit-ups can overstress the small facet joints of the lower spine which by the nature of their orientation prohibit rotation of the spine, thereby risking strain of the facet joints and overstressing the obliquus externus and obliquus internus muscles, resulting in soreness and pain in the rib walls. This case is most exaggerated when the spine is postured in the extremes of extension of flexion ranges of motion.
Therefore, to minimize the risk of injury as well as achieve a greater level of comfort and control compared to that resulting from performing abdominal exercises while lying on the floor, there has been a need for a device and/or technique whereby a person sitting in a chair can use the crunch motion while performing repetitions of exercises equivalent to sit-ups, rotary sit-ups and/or knee-ups, but while remaining within safe limits of stress to the back and to the abdominal muscles.
Various resistance-type exercise devices for exercising abdominal muscles are known. However, it has been found that when a person undertakes a program of conditioning the abdominal muscles by systematic use of such a device, that person often soon abandons the program because the resistance is so great as to allow performing only a few repetitions before fatigue sets in, or so small that the muscles are not adequately stressed regardless of how many repetitions are done. Even if the resistance is initially in an appropriate range for a user's muscular strength, he or she may find that as his or her muscles become stronger through exercise, that a conditioning plateau is reached where the set resistance is insufficient to provide further strengthening, thereby necessitating a need for a means to progressively increase or vary the resistance.
As is well-known, the preferred method for strengthening muscles is exercise using progressively increasing resistance because this places increasing demand on muscles and prevents them from accommodating to a specific force. Thus, to enable a resistance-type device to be used effectively by people having different strength, and to enable an individual who progresses through an exercise program to remain challenged as his or her strength increases, there is also a need for an abdominal exercise device which not only meets the above-stated criteria, but also one in which resistance can be conveniently increased or decreased.
2. Description Of The Related Art
Devices for exercising the abdominal muscles are known. For example, U.S. Pat. No. 5,069,448 to Shyu discloses a device which in use a person sitting on a chair alternately bends and straightens as well as twists the upper portion of his body when moving and turning a handle upward and downward, the handle being attached to a piston rod within a pneumatic cylinder which is positioned vertically between the person's thighs.
U.S. Pat. No. 5,046,726 to Van Straaten discloses a device which in use a person sitting on a chair, standing, or lying on the back with knees bent, applies a pumping action to a plunger, compressing a spring in a cylinder positioned vertically between the thighs or pressed against the abdomen.
U.S. Pat. No. 5,071,119 to Johnson discloses a device which in use a person sitting on a chair with the chin at the height of a horizontal pushbar attached to a vertical column pivotally supported on the floor places the arms over the pushbar and pushes down against the resistive force of a spring in the column, while twisting the upper portion of the body to the right and left, and then slowly allows the spring's resistive force to push his trunk upward to resume the original upright position.
U.S. Pat. No. 4,863,162 to Neckamm, et al. discloses a spring-loaded piston and cylinder assembly device which during use a transverse handle bar attached to a rod is pushed through the spring-loaded pipe. The pipe is attached at its lower end to a transverse support rod resting on the thighs of the user, the rod being slidably disposed within the pipe.
These above-described devices constrain a person to execute what are largely linear vertical motions or other motions which deviate in some respects from the natural, complex curvature motions of the spine during bending, so that bending of the torso, at least at some points within the full range of motion, occurs at the hips rather than at the lower spine and stomach, thereby predominantly stressing the hip joint flexor muscles rather than the abdominal muscles in these ranges. These motions are in sharp contrast to the crunch motion in which the spine is flexed forward in a curling path, and which motion is fully permitted by the present invention over the entire range of motion of the spine. The abdominal muscles consequently do not receive optimum benefit from use of conventional exercise devices.